The present invention relates to a method for machining a wiring board with a laser beam for piercing holes such as a through hole, an inner-via hole, and a blind-via hole or the like in a wiring board which is so-called a printed board as well as a device for the same, and more particularly to a method for machining a wiring board with a laser beam for changing the converging characteristic thereof as well as a device for the same.
FIG. 14 is a simulated view for explanation of the conventional technology. In FIG. 14, designated at the reference numeral 1 is a laser oscillator, at 2 a laser beam oscillated from the laser beam 1, at 3a, 3b bend mirrors each for bending the laser beam 2 oscillated from the laser oscillator 1, at 4 an image transferring mask having an aperture smaller than that of a diameter of the laser beam in a central section thereof, at 5 a galvano-mirror, at 6 a transmission type of optical component such as an f-xcex8 lens, and at 7 a wiring board as an object to be machined.
In FIG. 14, a laser beam 2 oscillated from the laser oscillator 1 is bent by the bend mirror 3a and goes into the image transferring mask 4. At this point of time, the laser beam 2 has a diameter larger than the aperture diameter of the image transferring mask 4 and is taken out by a desired amount of energy or as a desired form of beam through the image transferring mask 4. The laser beam 2 having passed through the image transferring mask 4 is bent by the bend mirror 3b, guided to a specified position of the f-xcex8 lens 6 by the galvano-mirror 5, and also guided to the wiring board 7, whereby a hole is pierced through the wiring board 7.
It is well known that a laser beam has a different intensity distribution, as indicated by reference signs xcex1, xcex2, xcex3 shown in FIG. 15A, according to a position after the laser beam is passed through the lens. Namely, FIG. 15A shows a laser beam 2 at each of the positions indicated by the reference signs xcex1, xcex2, xcex3 after the beam is passed through the f-xcex8 lens 6, FIG. 15B shows a beam intensity distribution at each of the positions such as at a position indicated by xcex1, namely a focal position, at a position indicated by xcex2, and at a position indicated by xcex3 each shown in FIG. 15A, and FIG. 15C is a view showing a form of a machined hole in the wiring board 7 at each of the positions indicated by xcex1, xcex2, xcex3 shown in FIG. 15A according to each beam intensity.
Generally, in a case where hole-piercing is executed in the wiring board 7, the wiring board 7 is placed at a position indicated by a in FIG. 15A, namely at a focal position. In this case, the intensity distribution of the laser beam 2 is flat as shown in FIG. 15B, and as a result, it is possible to machine a hole with a high degree of roundness and is straight in the direction of the board thickness of the wiring board 7 therein as indicated by xcex1 in FIG. 15C.
On the other hand, in a case where the wiring board 7 is placed at a position indicated by xcex2 in FIG. 15A, this situation is called a defocusing state, and the laser beam 2 is irradiated to the wiring board 7 as indicated by xcex2 in FIG. 15B with the intensity distribution thereof like that by the laser beam 2 with reduced converging characteristic, and for this reason it can be recognized that a tapered hole in which the diameter is large in the upper side of the hole and is small in the lower side thereof is formed, as indicated by xcex2 in FIG. 15C.
Further, in a case where the wiring board 7 is placed at a position indicated by xcex3 in FIG. 15A, the intensity distribution of the beam is like that by r in FIG. 15B, and a tapered angle of the machined hole can be increased as indicated by xcex3 in FIG. 15C. As described above, it is possible to easily change a tapered angle of a machined hole according to increase or decrease of a defocusing rate, so that in recent years, this method has become more and more popular and been used for actual industrial purposes.
In a case where the board is machined in the defocusing state, however, a degree of roundness of a machined hole therein is degraded due to astigmatism in a transmission type of optical components such as an f-xcex8 lens or the like.
It is also difficult to vertically adjust the axis of the laser beam after passing through the f-xcex8 lens to the wiring board in the area covering all inciding positions of the laser beam to the f-xcex8 lens, and for this reason, a positional displacement of a machined hole is generated even if the identical position is tried to be machined in a case of machining the hole at the focal position as well as in a case of machining it in the defocusing state. Accordingly, it is required to correct a positional displacement each time when the defocusing rate is changed, which causes increase of needless works.
It is an object of the present invention to provide a method for machining a wiring board with a laser beam in which the converging characteristic of a laser beam can be changed so that a desired tapered angle can be made in a hole to be machined as well as a device for the same.
A method for machining a wiring board with a laser beam according to the present invention, machines a wiring board by irradiating a laser beam onto a light shielding body provided in a light path between a laser oscillator and a machining lens for shielding a portion of said laser beam, and by introducing a non-shielded portion of said laser beam having passed through said light shielding body to said machining lens.
A device for machining a wiring board with a laser beam according to the present invention, comprises a light shielding body provided in a light path between a laser oscillator and a machining lens for shielding a portion of said laser beam, and a means for introducing a non-shielded portion of said laser beam having passed through said light shielding body to said machining lens.
A device for machining a wiring board with a laser beam according to the present invention, a light shielding body comprises a member which shields a central portion of a laser beam.
A device for machining a wiring board with a laser beam according to the present invention, a light shielding body comprises a member which shields a laser beam in an annular form.
A device for machining a wiring board with a laser beam according to the present invention, a light shielding body comprises a member which can change an area of a laser beam to be shielded.
A device for machining a wiring board with a laser beam according to the present invention, holds a light shielding body by a positioning means movable in the axial direction of a laser beam.
A device for machining a wiring board with a laser beam according to the present invention, comprises a means for changing a diameter of a laser beam inciding into a light shielding body.
A device for machining a wiring board with a laser beam according to the present invention, has the configuration in which a specified area to be shielded, a position of a light shielding body, or a diameter of a laser beam can be adjusted according to an instruction from a control unit.
A device for machining a wiring board with a laser beam according to the present invention, comprises a means for cooling a light shielding body.
A device for machining a wiring board with a laser beam according to the present invention, a light shielding body comprises a laser beam reflecting member with a laser beam damper provided therein.
Other objects and features of this invention will become understood from the following description with reference to the accompanying drawings.